Receiving apparatus for communication systems



Patented Apr. 7, 1942 TES RECEIVING APPARATUS FOR COMMUNI- CATION SYSTEMS Andrew J. Sorensen, Edgewood, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application June 21, 1941, Serial No. 399,136

9 Claims.

My invention relates to receiving apparatus for communication systems, and more particularly to receiving apparatus for communication systems for railway trains.

In communication systems of the type here contemplated, a carrier current is used. For telephone communication a carrier is modulated by the voice frequencies and a preselected side band of such modulated current is transmitted,

the carrier and the other sid band being preferably suppressed. At the receiving station such carrier telephone current is demodulated and current of the voice frequencies is supplied to a telephone receiver or a loud speaker. In such systems a calling or signaling current is needed and is usually effected byfprcducing a current equivalent to the carrier modulated by a preselected frequency within the voice frequency range or modulated by a preselected relatively narrow band of voice frequencies. 'ing station, the receiving apparatus includes a At the receivfilter tuned sharply to such preselected band or single frequency and which is connected to the output terminals of the demodulator for passing current of such preselected frequency to special calling and signaling apparatus with the result that the receiving station is provided with an in.- dication when telephone communication is desired. In such communication systems for railway trains the calling or signaling current'is in :1

'must be non-responsive to energy of the preselected voice frequency occurring in the telephone current and must also be non-responsive to voltage surges created by extraneous magnetic fields.

Accordingly, a feature of my invention is the provision of receiving apparatus for communication systems incorporating novel and improved means responsive to a calling or signaling current.

Another feature of my invention is the provision of receiving apparatus for communication I systems of the type here involvedincorporating When in such systems for railnovel means including an electromagnetic relay that is effectively energized by the signaling current energy appearing at the output terminals of the demodulator and additional amplifiers and sources of current are not required.

A further feature of my invention is the provision in receiving apparatus for communication systems of the type here contemplated of novel and improved signaling apparatus incorporating means that discriminates against voltage surges of short duration, but an application of voltage of greater duration, even though of lesser magnitude than the surge voltage, operates the signaling apparatus.

Again, a feature of my invention is the provision of receiving apparatus for communica-- tion'systems incorporating novel and improved delay means for the signaling portion of the apparatus and wherewith a substantially uniform predetermined delay period is effected in the operation of the signaling means even when the signaling current frequency repeatedly occurs in the telephone current.

Again,'a feature of my inventionis the provision in receiving apparatus for communication systems for railway trains of 'calling'and signaling means requiring relatively few parts and'that is relatively low in cost.

Other features, objects and advantages of my invention will appear as the specification progresses.

The above features, objects and advantages of my invention I attain by providing an electromagnetic relay characterized by a relatively high sensitivity and which is connected to the output terminals of the demodulator through a rectifier and a filter tuned to pass current of a preselected frequency within the voice frequency range only, or at least to pass only a relatively narrow band of frequencies within the voice frequency range. The signaling current to be used in such a system is then made to have such preselected frequency or narrow band of frequencies and the relay is effectively energized and picked up in response to current of such preselected frequency or band offrequencies appearing at the output terminals of the demodulator and additional amplification and current sources are not required. A surge protector is preferably interposed in the connection of the rectifier to the filter to dis criminate against voltage surges but to cause little attenuation to sustained fiow of the signaling current.

Another relay is controlled over a front contact of the firstmentioned relay, and the two ceived and being switched to an active condition when such current ceases.

A delay means in the form of a resistor and two condensers is associated with the two relays so that operation of the indication means is effected only after the signaling current is received for a predetermined time interval and such operation of the indication means is not effected due to energy of the preselected frequency occurring in the telephone current. A circuit arrangement is also including in the apparatus for quickly discharging a selected one of the condensers so that a charge cannot be built up on the condenser to cancel or shorten the predetermined delay period byrepeated operations of the first mentioned relay because of repeated occurrences of the signaling frequency in'the telephone current or because of repeated voltage surges. I

The delay means associated with the control relays of my present application is similar to the delay means of my copending application for Letters Patent of the United States, Serial No.

372,902, filed January 2, 1941, for Receiving ap-' paratus for train communication systems, and in which copending application such delay means is claimed broadly.

I shall describe one form of apparatus embodyingmy invention and shall then point out'the novel features thereof in claims.

The accompanying drawing is a diagrammatic view showing a preferred form of apparatus embodying my invention when used for a communication system for a railway train. It will be understood, however, that my invention isn'ot limited in itsuse to communication'systems for id railway trains and this one application will serve to illustrate the many places such apparatus is useful.

Referring to the drawing, the reference character IC designates an inductor mounted on a vehicle of a railway train ininductive relation to a transmitting circuit, not shown. Ordinarily, inductor IC is mounted on the train in inductive relation to the trackrails since the track rails are preferably included in the transmitting a: 1 circuit to which communication current is sup- 1 plied at a station remote from the vehicle on which the apparatus of the drawing is mounted.

' Such transmitting circuit may be, for example,

that covered by the Letters Patent of the United States No. 2,112,364, granted March 29, 1938, to L. O. Grondahl, for Electric train signaling system.

The electromotive forces induced in inductor 10 in response to current flowing in the associated transmitting circuit are applied to the input side of an amplifier-demodulator AD. The amplifier-demodulator AD may be any one of several well-known types of such devices and is shown conventionally for the sake of simplicity since its specific structure forms no part of my present invention. It is suificient for this application to point out that amplification and demodulation is effected by the device AD when a modulated carrier currentis applied to its input terminals and current of the modulating frequency appears at its output terminals. For ex ample, it has been proposed for communication systems for railways to employ for telephone communication the upper side band of a carrier 0f 5700 cycles per second modulated by voice frequencies of the range of 500 to 2500 cycles per ,to 8200 cycles per second. For calling and sig- "naling purposes, a current of the order of 6700 second. That is to say, the current transmitted over the transmitting circuit is a suppressed carrier upper side band telephone current of 6200 cycles-per second is used, such current being. the

equivalent of the upper side band of .the carrier of 5700 cycles modulated by the preselected voice frequency of 1000 cycles. Thus when electromotive forces of a frequency corresponding to I that of the telephone current is induced in inductor 10 current of the voice frequencies of 500 to 2500 is supplied to the output'terminals 'of the demodulator, and when an electromotive force corresponding infrequency to that of the signaling current of 6700 cycles is induced in inductor 10 a signaling current of 1000 cycles is supplied to the output terminals of the demodulator.

A'filter Fl including a reactor 34, a condenser I3 and a transformer TI is coupled to the output side of the amplifier-demodulator AD by primary winding [4 of transformer TI being connected across the output terminals of the demodulator. The parts are so proportioned that filter Fl is tuned sharply to the preselected frequency of the signaling current, that is, it is tuned to pass only energy of 1000 cycles persecond when signaling current of the frequency referred to hereinbefore is used. Thus, by transformeraction, the signaling currentis transferred from the output terminals of the amplifier-demodulator to secondary winding I5 of transformer TI and telephone current of the voice frequenciesof 500 to 2500 cycles per second is suppressed insofar as being supplied through filter Fl except when the voice frequency of 1000 cycles per second occurs in the telephone current. I

An electromagnetic relay RI is connected to secondary winding I5 of transformer Tl through a full waverectifier I6. A surge protector or variable resistor TH, preferably of the type designated by the trade name 'Ihermistor is interposed in the connection of rectifier I6 to secondary winding I5. Surge protector or va'riablercsistor TH is characterized by thermal inertia and high initial resistance and substantially blocks or discriminates against voltagesurges of short duration, but an application of such'voltage of greater duration even though of lesser magnitude than the surge voltage is passed with little attenuation after a small delay.

Electromagnetic relay RI is preferaby of the polar type operated by direct current of one polarity only, and is characterized by a high sensitivity- For example, relay RI may be of the type covered by a co-pending application for Letters Patent, Serial No. 365,039, filed Novemher 9, 1940, by R. M. Laurenson, for Electrical relays. Relay BI is connected to the output terminals of rectifier I6 to be energized by the current passed by filter FI, and it follows that IC,' but that relayRl remains deenergized and period of relay R2. When relay R2 is released,

device TH, with the result that energy of the preselected voice frequency used for the signaling current when occurring in a telephone current is blocked from reaching relay RI, and also that Voltage surges induced in inductor 10 due to extraneous magnetic fields are blocked by device TH.

Relay RI when picked up to close its front contact I1, completes an energizing circuit for another relay R2 which is preferably of the direct current type and which is effectively energized by current from a direct current source whose terminals are indicated at B and C.

Condensers CI and C2, and a resistor 32 are associated with relay R2 to efiect a delay period in the operation of that relay. Condenser C2 is permanently connected across the winding of relay R2. Condenser CI is also connected across the winding of relay R2 over a connection including front contact 35 of relay RI and back contact 2| of relay R2 as will be apparent from an inspection of the drawing. Thus, when relay RI is picked up to close front contacts I! and 35, a circuit is formed from terminal'B over front contact I! of relay RI, resistor 32, winding of I relay R2 in multiple with both condensers CI and C2 and thence to terminal C of the current source. Relay R2 is energized and picked up only after a delay period predetermined by the size of resistor 32 and by the capacity of the con- 5 densers CI and C2, since it is necessary that condensers CI and C2 be first charged before the relay R2 is effectively energized. The parts are so proportioned that condenser CI is relatively large and provides a relatively long delay period in th picking up of relay R2. Condenser CI is disconnected from the energizing circuit of relay R2 when that relay picks up to open its back contact 2|, and hence when relay RI is released to open the energizing circuit of relay R2, relay R2 is retained energized for a period predetermined by the capacity of condenser C2, since condenser C2 discharges through the windingof relay R2 to retain that relayenergized. It is to be observed that when both relays RI and R2 are released, condenser CI is provided with a discharge circuit including back contact 2| of relay R2, a resistor 22 and back contact 23 of relay RI.

Relays RI and R2 jointly control the connection of a loud speaker LS to the terminals of the amplifier-demodulator AD, and an indication means comprising two lamps LI and L2 and a bell BI. With relay R2 picked up a circuit is formed from terminal B over front contact 2? of relay R2. lamp LI and to terminal C, and lamp vLI is illuminated. Relay R2 when released completes a circuit including terminal B, back contact 28 of relay R2, lamp L2 and terminal C, and lamp L2 is illuminated. Subsequent to the release of relay RI and befor relay R2 is released at the end of its slow release period as effected by condenser C2, a circuit is formed from terminal B over front contact 21 of relay R2, back contact 29 of relay RI, bell BI and to terminal C, and

the bell BI is sounded during this slow release closing back contact 30, the operating winding of the loud speaker LS is connected across the output terminals of amplifier-demodulator AD over a circuit easily traced.

In describing the operation of the apparatus, I shall assum that at the start relays RI and R2 are deenergized and the associated remote control station starts supplying signaling current to the transmitting circuit causing a sustained electromotive force of the frequency corresponding to the frequency of the signaling current to be induced in inductor IC. For example, such signaling current may be of 6700 cycles per secend as referred to hereinbefore. The electromotive force is amplified and demodulated and signaling current of 1000 cycles per second is supplied from the output terminals of the amplifierdemodulator AD through filter FI,:to rectifier 56, there being a brief delay in the application of the energy to the rectifier I6 due to the action I of device TH. This signaling current is rectified and applied to relay RI, causing relay RI to be eifectively energized and picked up. Relay RI on picking up to close front contacts I1 and 35 completes the energizing circuit for relay R2 and the connection of the condenser CI to relay R2 and that relay is picked up after condensers CI and C2 have been charged through resistor As stated hereinbefore, condenser CI is of relatively large capacity and hence provides a relatively long predetermined delay period in the picking up of relay R2. After relay R2 is picked up, condenser C2 is disconnected and relay R2 is then retained energized in multiple withcondenser C2. Relay R2 on picking up to close front contact 2'! causes lamp LI to be illuminated as an indication that signaling current is being received. With the signaling current continuously transmitted, lamp LI is continuouslyilluminated and forms an indication that the system is in working order. The loud speaker LS is now disconnected from the amplifier-demodulator and is in an inactive condition.

In the event the operator of the associated remote station desires to initiate telephone communication with the operator at the station of the receiving apparatus of the drawing, the operator at the remote'station discontinues the sending of the signaling current with the result that relayRI is at once deenergized and released. ,lcla'y R2 is retained picked up until condenser C2 is discharged and during the interval that relay R8 is released and relay R2 is picked up, the bell BI is sounded as anjaudible indication that telephone communication can be expected. With relay R2 released at the end of its slow release period, the sounding of bell B; is interrupted, lamp LI is extinguished, lamp L2 is illuminated and loud speaker LS is connected to the output terminals of the amplifier-demodulator. The illumination of lamp L2 is' an additional indication that telephone communication can be expected and in the event lamp L2 remains illuminated and no telephone current is shortly received, then lamp L2 serves to indicate an inoperative condition of the system, the

'electromotiye forces induced in inductor 10 cause telephone current to appear at the output terminals of the demodulator, and the voice frequencies are reproduced at the loud speaker LS.

.Such telephone current will not be passed by filter FI rexceptas the preselected frequency of 1000. cycles may. occur in the telephone current.

Such'occurrence of energy of 1000'cycles in the telephone current would; be ordinarily, of short duration and would ordinarily be blocked by the 'ly.,picked'up, it is to be noted that the condenser CI isdischarged each'time that relayRI ,is'released due to'the discharge circuit including backfcontacts 2| and 23 of the two relays, with theuresult that the predetermined delay period in the picking up of relay R2 is effected each time that relay RI is picked up. In other words, repeated picking up of relay RI does not cause a'charge to be built up on condenser CI that will eventually defeat thedelay period effected in the picking up of the second relay R2.

When telephone communication is terminated then the associated remote station would again send the signaling current with the result that the-apparatus is restored to its normal condition, that is, to the condition illustrated in the drawing.

From the foregoing description it is clear that I have providedreceiving apparatus for a com- ,municationsystem incorporating signaling and indication means of relatively simple construction and that is free from operation due to surge voltages and from the telephone current. It is to be observed that the surge protector ,TI-I may be omitted and the delay period provided for relay R2 relied upon to avoid operation of the indication devices in response to surge voltages ing a condenser'associated with said indication means to avoid the establishing of said predetermined condition of the indication means for a given delay period-when current is passed by said filter, and means including a contact of said relay to discharge said condenser to assure said given delay period when current is repeatedly passed by said filter.

'2. In receiving'apparatus for a communication system using a carrier telephone current and a signaling current equivalent to the carrier modulated by a preselected voice frequency, the combination comprising, a'demodulator arranged to receive such currents and operative to cause current of the voice frequencies to appear at its output terminals when the telephone current is received and to cause a current of said preselected frequency to appear at its output terminals when the signaling current is received, a

direct current relay, circuit means including a filter tuned to pass only current of said preselected frequency and arectifier to connect said relay to the demodulator output terminals for energization of the relay when said signaling current is received, indication means controlled by said relay and operable to a predetermined condition when the relay is energized, means including a condenser controlled over contacts of said relay to prevent theestablishing of said predetermined condition of the indication means for a given delay period when current is passed by said filter, and a discharge circuit including a contact of said relay to discharge said condenser to assure substantially the same said given delay period each successive time current is passed by said filter,

3; In receiving apparatus for a communication system using a carrier telephone current and a signaling current equivalent to the carrier modulated by 'a preselected voice frequency, the com- .bination comprising, a demodulator arranged to receive such currents and operative to cause ourrent-of the voice frequencies to appear at its outand to energy of the signaling frequency occurring in the telephone current.

Although I have herein shown and described only one form of receiving apparatus for communication systems embodying my invention, it

is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I.

claim is:

1. In receiving apparatus for a communication system using a carrier telephone current and a signaling current equivalent to the carrier modulated by a preselected voice frequency, the combination comprising, a demodulator arranged to receive such currents and operative to cause current of the voice frequencies, to appear at its output terminals when the telephone current is received and to cause a current of said preselected frequency to appear at its output terminals when the signaling current is received, a direct current relay, circuit means including a filter tuned to pass only current of said preselected frequency and a rectifier to. connect said relay to the demodulator output terminals for energization of the relay when said signaling current v is received, indication means controlled by said relay and operable to a predetermined condition when the relay is energized, delay means includ-- put terminals when the telephone current is ree ceived and to causea current of'said preselected frequency to appear at its output terminals when the signaling current is received, a direct current relay, circuit means including a filter tuned to pass only current of said preselected frequency and a rectifier'to connect said relay to the de- ,modulator output terminals for energization of the relay when said signaling current is received, another relay controlled over a front contact of the first mentioned relay, aloud speaker coupled to the outputterminals of said demodulator over a-back contact of said other relay, a condenser connected to said other-relay over a front contact of the first mentioned relay to introduce a given delay in the picking up of said other relay and a discharge circuit including a back contact of the first mentioned relay for said condenser to assure such delay period when current is intermittently passed by said filter.

4. In receiving apparatus for a communication system usinga carrier telephonecurrent and a signaling current equivalent to the carrier modulated-by a preselected voice frequency, the com- ;bination comprising, a demodulator arranged to receive such currents and operativeto cause current of the voice frequencies to appear at its output terminals when the telephone current is received and to cause a current of said preselected frequency to appear at its output terminals when the signaling current is received, a direct current relay, a filter proportioned to pass only current of said preselected frequency, a surge protector characterized by high initial resistance and a relatively low resistance after current is applied thereto for a period; circuit means including said filter and said surge protector to connect said relay to the output terminals of the demodulator to energize and pick up the relay when sustained signaling current is received but to block current from the relay when telephone current is received, and indication means controlled over a front contact of said relay.

5. In receiving apparatus for a communication system using a carrier telephone current and a signaling current equivalent to the carrier modulated by a preselected voice frequency, the combination comprising, a demodulator arranged to receive such currents and operative tocause current of the voice frequencies to appear at its output terminals when the telephone current is received and to cause a current of said preselected frequency to appear at its output terminals when the signaling current is received, a direct current relay, a filter proportioned to pass only current of said preselected frequency, a surge protector characterized by a high initial resistance and a relatively low resistance after a sustained fiow of current; circuit means including said filter, said surge protector and a rectifier to connect said relay to the output terminals of the demodulator to energize and pick up said relay by a sustained flow of the signaling current and to avoid picking up of the relay by energy of said preselected frequency occurring in the telephone current; a loud speaker, an indicator,and circuit means controlled by said relay to connect the loud speaker to the demodulator and deenergize the indicator when the relay is released and to disconnect the loud speaker and energize the indicator when the relay is picked up.

6. In receiving apparatus for a communication system using a, carrier telephone current and a signaling current equivalent to the carrier modulated by a preselected voice frequency, the combination comprising, a demodulator arranged to receive such currents and operative to cause current of the voice frequencies to appear at its output terminals when the telephone current is received and to cause a current of said preselected frequency to appear at its output terminals when the signaling current is received, a direct current relay, a filter proportioned to pass only current of said preselected frequency, a surge protector characterized by a high initial resistance and a relatively low resistance after a brief delay when a sustained flow of current is effected; circuit means including said filter, said surge protector and. a rectifier to connect said relay to the output terminals of said demodulator to energize and pick up said relay when sustained signaling current is received and to avoid energizing the relay by a surge voltage due to an extraneous magnetic field or said preselected frequency occurring in a telephone current; indication means controlled over a front contact of said relay, and a delay means including a condenser associated with said indication means to delay its response to the closing of said front contact.

'7. In receiving apparatus for a communication system using a carrier telephone current and a signaling current equivalent to the carrier modulated by a preselected voice frequency, the combination comprising, a demodulator arranged to receive such currents and operative to cause current of the voice frequencies to appear at its output terminals when the telephone current is received and to cause a current of said preselected frequency to appear at its output terminals when the signaling current is received, a direct current relay, circuit means including a filter tuned to pass only current of said preselected frequency and a rectifier to connect said relay to the demodulator output terminals for energization of the relay when said signaling current is received, an-

other relay, a first condenser, a second condenser permanently connected across the Winding of said other relay, a resistor, a source of direct current, means including a back contact of said other relay and a front contact of the first mentioned relay to connect said first condenser across the winding of said other relay; an energizing circuit including said current source, a front contact of the first mentioned relay, said resistor and the winding of said other relay to pick up said other relay after a, delay period predetermined by the time required to charge the first and second condenser in multiple through said resistor; said lated by a preselected voice frequency, the combination comprising, a demodulator arranged to receive such currents and operative to cause current of the voice frequencies to appear at its output terminals when the telephone current is received and to cause a current of said preselected frequency to appear at its output terminals when the signaling current is received, a direct current relay, circuit means including a filter tuned to pass only current of said preselected frequency and a rectifier to connect said relay to the demodulator output terminals for energization of the relay when said signaling current is received, another relay, a first condenser connected across the winding of said other relay over a back contact of said other relay and a front contact of the first mentioned relay, a second condenser permanently connected across the winding of said other relay, a first resistor, a direct current source; an energizing circuit including said current source, afront contact of the first mentioned relay, said resistor and the winding of said other relay to pick up said other relay with a slow pick-up period equal to the interval required to charge said condensers and to release said other relay with a slow release period equal to the interval required to discharge the second condenser through the winding of said other relay; a first indicator controlled over a front contact of said other relay, 9, second indicator controlled over a front contact of said other relay in series with a back contact of the first mentioned relay, and a loud speaker connected to the output terminals of the demodulator over a back contact of said other relay.

9. In receiving apparatus for a communication system using a carrier telephone current and a signaling current equivalent to the carrier modulated by a preselected voice frequency, the combination comprising, a demodulator arranged to receive such currents and operative to cause current of the voice frequencies to appear at its output terminals when the telephone current is received and to cause a current of said preselected frequency to appear at its output terminals when the signaling current is received, a direct current relay, circuit means including a filter tuned .to

relay, said resistor and the winding of said other arr-@184 relay to pick up said other relaywith a slow pickup period equal to the interval required to charge said condensersand to release saidother' relay with a slow release period equal to the interval required to discharge the second condenser through the winding of said other relay; a discharge circuit for said first condenser including a back contact of said other relay and a backbontack of the'first mentioned relay to maintain the slow pick-up period of said other relay substantially uniform when current is repeatedly passed bythe filter, a first indicator controlled over a front c'ontact'of said other relay, and a second indicator controlled over a front contact of said other relay in series with a back contact of the first mentioned relay.

l ANDREW J. SORENSEN. 

